0000 Programming

#include <stdio.h>
#include <string.h>

const int N = 12;     // essential of number
int main() {
    char a[N], b[N];
    int result[N];

    //------------------- initial  value -------------------
    for (int i = 0; i < N; ++i) {
        a[i] = b[i] = '0';
        result[i] = -1;
    }

    //------------------------ input -----------------------
    scanf("%s %s", a, b);

    // --------- find length of string 'a' and 'b' ---------
    int len_a = strlen(a);
    int len_b = strlen(b);

    int i;
    //-------------- swap string 'a' and 'b' ---------------
    for (i = 0; i < len_a/2; ++i) {
        char c = a[i];
        a[i] = a[len_a - i - 1];
        a[len_a - i - 1] = c;
    }
    for (i = 0; i < len_b/2; ++i) {
        char c = b[i];
        b[i] = b[len_b - i - 1];
        b[len_b - i - 1] = c;
    }

    //------------ calculate plussing - processing ----------
    i = 0;
    while (i < len_a && i < len_b) {
        result[i] = a[i] - '0' + b[i] - '0';
        ++i;
    }
    while (i < len_a) {
        result[i] = a[i] - '0';
        ++i;
    }
    while (i < len_b) {
        result[i] = b[i] - '0';
        ++i;
    }
    int tod = i = 0;
    int ans[N];
    int ans_i = 0;
    while (result[i] != -1) { // using array to be stack
        ans[ans_i++] = (result[i]+tod) % 10;
        tod = (result[i]+tod) / 10;
        ++i;
    }
    if(tod > 0)ans[ans_i++] = tod;

    //--------------------- output --------------------------
    while (--ans_i >= 0) {
        printf("%d",  ans[ans_i]);
    }
}